One technology that is concerned with electric vehicles is a technology for controlling a propulsive motor (electric motor). See, for example, U.S. Pat. No. 5,367,455 (hereinafter referred to as “U.S. Pat. No. 5,367,455A”) and Japanese Laid-Open Patent Publication No. 06-121405 (hereinafter referred to as “JP06-121405A”).
According to U.S. Pat. No. 5,367,455A, the maximum speed of an electric vehicle is limited based on a traveling state and a manipulated state of the vehicle, and a remaining battery power level (see, column 6, line 29 through column 7, line 58, and FIGS. 2 through 10). More specifically, a condition is set as to whether a maximum speed control process, an acceleration control process, or both of such processes should be performed, based on the traveling state and manipulated state of the vehicle (see, column 6, line 64 through column 7, line 7, and FIG. 10). In addition, if the maximum speed control process is performed, then a maximum limit speed (V0) is set depending on the remaining battery power level (DODs) (see, column 6, lines 29 through 34, and FIG. 7(a)). If the remaining battery power level drops to a preset value (DOD1) (S31: YES), and if the driver enters a signal indicating that a traveling performance limit control process should be performed (S34: YES), then the maximum speed control process is performed depending on the settings (S39: YES, and subsequent steps) (see, column 7, line 44 through column 8, line 14).
According to JP06-121405A, an electric vehicle is disclosed, which is capable of selecting a driving performance-oriented power mode and a highly efficient driving-oriented economy mode (see, paragraph [0006]). More specifically, a field current is set depending on the rotational speed of an AC motor in the power mode, and a field current is set depending on the torque command in the economy mode (see, Abstract). For switching between the power mode and the economy mode, a mode switching device (13) may be used (see, paragraph [0007]), or an automatic mode switcher (22) may be used (see, paragraph [0012]). When the mode switching device is used, a low-pass filter (20) prevents a field current command from changing too quickly (see, paragraph [0010]). For switching between traveling modes, the automatic mode switcher weights the economy mode and the power mode depending on a depth to which the accelerator pedal is depressed (see, paragraph [0012]). In addition, a membership function may be used to smoothly switch between traveling modes (see, paragraph [0012]).
A practice also is known in which three or more traveling modes are provided. See, for example, Japanese Laid-Open Patent Publication No. 2007-302055 (hereinafter referred to as “JP2007-302055A”).